This project will examine metabolic, physiological and consequent fitness-related effects in vivo of naturally occurring genetic polymorphism in enzymes of glycolysis. An insect study system (genus Colias; Lepidoptera, Pieridae) will be used. We have already begun to document in vivo effects, at all organizational levels, of a major polymorphism at the phosphoglucose isomerase (PGI) locus. We will complete documentation of this variation's effects on glycolytic intermediate pool sizes, changes in flux through this pathway, etc. in relation to relevant biological variables such as temperature and activity demand. Physiological consequences for flight capacity, and entailed changes in survivorship, flight activity, mating success, and mate choice in the wild will all be documented. Genetic variation at additional glycolytic loci will be put to similar examination as knowledge of it is developed. Available analytical or simulation models will be used or extended to establish continuity of effects among different levels of organization. The overall results will advance understanding of allozyme polymorphisms, lead to progress in evolutionary genetics, and clarify the possible importance of allozyme variation for public health, in direct application to human genetics and indirectly via agricultural implications.